1. Field of the Invention
The invention relates to a cutting insert, in particular an indexable insert for cutting metal workpieces, with a cover surface, a cutting edge and a chip flute adjacent to the cutting edge made in the face of the cutting edge to form and guide the chip that is discharged. Such cutting inserts are mounted interchangeably on tool holders. The basic shape of conventional cutting inserts of this type has two opposite cover surfaces that are parallel to each other with a polygon-shaped peripheral wall between them. The cutting edges are formed by the transition edges between the respective cover surfaces positioned at the top and the flat areas of the peripheral wall of the insert. Two transition edges meeting at an angle form a rounded cutting tip where they join. Thus, the cutting inserts have an essentially triangular, quadrangular, rhombic or otherwise polygonal contour. This makes it possible to provide the cutting inserts with a plurality of cutting edges or cutting tips that can be brought into their engagement position one after the other on a holder. Such cutting inserts are referred to as indexable inserts. They make possible better utilization of the quantity of material required for the cutting insert and thus provide cost savings.
2. Background Information
The cover surface, which is on top when the cutting insert is clamped onto the holder and comes into contact with the chip during the cutting process, comprises or is the face of the cutting edge that is adjacent to it. The side faces of the cutting insert form the flanks of the cutting edges that delimit them toward the cutting side in the operating position. During the cutting process, the flank of a cutting edge with its respective surface faces the workpiece to be machined. The surface of the workpiece being machined passes along the flank of the major or minor cutting edge of the cutter cutting tip which is in the cutting engagement position in the direction facing away from the cutting edges at an angle that forms the clearance angle. Typical cutting inserts of this type are known, for example, from U.S. Pat. Nos. 4,880,338, 4,335,984, 4,988,242 and 4,215,957, which are incorporated by reference herein.
The geometry of the cutting edges of such cutting inserts is determined by the desire to minimize the energy required for the cutting process. The energy is determined by the geometry of the chips generated, and their geometry depends on the geometry of the cutting inserts or their cutting edges. Also important for chip formation are the cutting speed, the feed, and the depth of cut. The faces are frequently provided with flutes in the areas flanking the cutting edges to control chip flow and to influence the shape of the chips as they are removed and flow away from the workpiece. The invention relates to the shape of such chip flutes flanking a cutting edge which are formed in at least one face of such a cutting insert.
It is considered advantageous if the chip removed by the cutting edge, viewed crosswise to its direction of flow, is asymmetrically concave, is curved in an oval shape, and if this chip, viewed in its longitudinal direction, i.e. in the direction of the chip flow directed away from the cutting edge, comprises scales, as it were, which are fitted together in the direction of the chip flow. This structure facilitates chip breakage and also helps to achieve the objective of the configuration of the cutting insert according to the invention.
Thus, the object of the invention is to design the initially mentioned cutting insert such that it ensures an advantageous cutting process or chip removal. This object is achieved in a cutting insert, particularly an indexable insert for removing chips during the machining of metal workpieces. The cutting insert has at least one cutting edge and at least one chip flute flanking the cutting edge made in the face to shape and guide the chip that has been separated and is being removed from the workpiece. The surface of the chip flute is realized similar to the surface of an asymmetrical oval hollowed-out shell, whereby the asymmetry of the oval curved shape of a profile cross section of the shell surface comprises a profile cross section in the direction of the major axis and minor axis that has a curvature which is less pronounced on its side facing the cutting tip and the cutting edge than on its side facing away from the cutting tip and the cutting edge. The term xe2x80x9covalxe2x80x9d is derived from the Latin word xe2x80x9covumxe2x80x9d meaning egg. It describes a closed flat curve with positive curvature throughout, which as a rule has four vertices. The oval can thus be defined loosely as an ellipse (a. Brockhaus Encyclopedia, Vol. 24-19th Edition, 1991).
The embodiment of a chip flute according to the invention and its correspondence with the geometry of the cutting insert have the effect that the chip does not run off essentially perpendicular to the cutting edge, particularly to the major cutting edge, but is deflected away from the cutting edge at an acute angle, the angle sides of which diverge in the direction facing away from the cutting tip. The cutting tip is the part of the cutting tool that is closest to the workpiece during the cutting process. If the chip flow direction is influenced in such a way that it points away from the workpiece, if possible as soon as when the chip is created, the workpiece is optimally protected from damaging effects. On the other hand, a chip that normally strikes a straight or symmetrically curved cutting edge moves away from the cutting edge approximately perpendicular to the cutting edge, and that is what this invention aims to prevent. The cutting insert geometry responsible for this effect has also an advantageous effect on the speed with which the chip is removed. In the narrower area taught by the invention facing the cutting tip, the chip flow is more severely restricted than in the area facing away from the cutting tip, in which the chip flute is wider.
Whether the cross-sectional profile of the chip flute surface has a greater or lesser curvature in the respective directions of the major and minor axis of the oval shape on its side facing the cutting tip and the cutting edge, compared to the side facing away from the cutting tip, essentially depends on the material. The more pronounced curvature is particularly suitable for a hard material and the less pronounced curvature for a soft material.
According to a further development of the invention, the chip flutes designed according to the invention can be spaced at a varying distance from the associated cutting edge. Different positions are disclosed in the embodiments of the invention discussed herein below.
Advantageously, a plurality of chip flutes thus formed may be arranged end-to-end along the cutting edge like a strand of pearls. If these chip flutes are sized identically and arranged parallel to the cutting edge as discussed in the embodiments of the invention herein below, the chip is given a corrugated profile, the corrugations of which are asymmetrical and thus cause a flow away from the cutting tip. If, as disclosed in the embodiments of the invention discussed herein below, the chip flutes increase in size with increasing distance from the cutting tip, the above effect on the chip shape is significantly enhanced. Finally, at least one of the embodiments of the invention discussed herein below comprises a further development in that it places an additional central flute in the area of the cutting tip.
The asymmetry discussed above in relation to the perimeter edge of the chip flute may be further defined, in at least one possible embodiment of the present invention, by different radii of curvature of sections of the perimeter, which radii of curvature are different from or not equal to corresponding radii of curvature which may be located on an opposite side of the perimeter edge. For example, the radius of curvature of a first section of the perimeter that is immediately adjacent the cutting tip may be different from a second corresponding section disposed opposite the first section on the side of the perimeter disposed furthest from the cutting tip. Also, the radius of curvature of a third section of the perimeter that is immediately adjacent a cutting edge may be different from a fourth corresponding section disposed opposite the second section on the side of the perimeter disposed away from the cutting edge. Therefore, different radii of curvature of various sections of the perimeter edge will produce the asymmetry of one side or section with respect to an opposing or corresponding side or section.
In addition, the asymmetry may be further defined by the bisection, either lengthwise or widthwise, of the essentially oval-shaped chip flute. For example, a bisection line could be drawn along the length of the flute from two points which are the two points furthest apart from each other at opposite ends of the chip flute. The two halves produced by the bisection of the chip flute, in an asymmetrical arrangement, would not be mirror images of each other. One half could have a different curvature and/or perimeter length from the other. Further, in at least one embodiment, substantial portions of opposing sides would have a different curvature and/or perimeter length from each other to produce a substantial asymmetry with respect to each other. On the contrary, symmetrical halves would be essentially mirror images of each other. A similar line of bisection across the width and essentially perpendicular to the bisecting line of the length could also produce halves that are asymmetrical in that they are not mirror images of one another.
In a further possible embodiment according to the present invention, the cutting insert has two chip flutes located adjacent the cutting edges, which chip flutes are similar to each other. To further explain, the two chip flutes may have essentially identical perimeter edges. The chip flutes may also have similar depression surfaces in shape, slope, and/or depth. In another embodiment, the chip flutes may also be different in any one of the above features.
In at least one possible embodiment of the present invention, the essentially oval-shaped edge surrounding the perimeter of the chip flute may be substantially symmetrical, while the depth of the depression may be asymmetrical. To further explain, the deepest point of the chip flute may not be located in the geometric center of the depression; that is, the deepest point in the depression is located away from the geometric center of the depression and nearer to a point or area on the perimeter edge of the chip flute. Therefore, the slope of the surface of depression on the side nearest the cutting tip, for example, may be less than the slope of the surface of the depression on the opposite side furthest away from the cutting tip. The deepest point is the same distance in depth from any and all points on the perimeter edge of the chip flute, but is not the same distance in point-to-point length from all points along the perimeter edge of the chip flute. The deepest point may be located at any point on the surface of the depression within the depression.
In another possible embodiment according to the present invention, there may be several depressions or chip flutes that are connected together in a string or cascading arrangement. Each of the individual depressions may have any of the characteristics of the solitary depressions discussed above. The depressions may be connected by narrow plateaus or ridges, which are areas where the upwardly sloping sides of two adjacent depressions meet. These ridges may be of different shapes. In at least one possible embodiment of the present invention, the ridges may be curved such that the inside of the curve faces away from the cutting tip. Other configurations may have the inside of the curve facing toward the cutting tip. Still another variation might combine the two into an S-shaped curve.
The above-discussed embodiments of the present invention will be described further hereinbelow. When the word xe2x80x9cinventionxe2x80x9d is used in this specification, the word xe2x80x9cinventionxe2x80x9d includes xe2x80x9cinventionsxe2x80x9d, that is the plural of xe2x80x9cinventionxe2x80x9d. By stating xe2x80x9cinventionxe2x80x9d, the Applicant does not in any way admit that the present application does not include more than one patentably and non-obviously distinct invention, and maintains that this application may include more than one patentably and non-obviously distinct invention. The Applicant hereby asserts that the disclosure of this application may include more than one invention, and, in the event that there is more than one invention, that these inventions may be patentable and non-obvious one with respect to the other.